Knoevenagel condensation of the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione with 9-anthracenecarboxaldehyde: Synthesis of the second-generation ligand 2-(anthracen-9-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione

The Knoevenangel condensation between 9-anthracenecarboxaldehyde and the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione (bpcd) takes place rapidly in CH₂Cl₂/MeOH solution in the presence of molecular sieves (4 ?) to produce the functionalized ligand 2-(anthracen-9-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione. The title compound has been isolated and characterized in solution by IR, NMR, and UV-vis spectroscopies, and the solid-state structure has been established by X-ray diffraction analysis. 2-(anthracen-9-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione crystallizes in the triclinic space group P−1, a=10.227(2) ?, b=13.865(2) ?, c=15.905(2) ?, α=112.157(2)°, β=101.424(2)°, γ=100.065(3)°, V=1968.5(5) ?³, Z=2, and d _calc=1.101 Mg/m³; R=0.0873, R _w=0.2604 for 7452 reflections with I>2σ(I). The cyclic voltammetric behavior for 2-(anthracen-9-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione has been studied, and the observed redox data and results from extended Hückel MO calculations are discussed relative to the parent ligand bpcd.

Michael G. RichmondEmail: